Many electronic components including an IC, LSI or the like in which a semiconductor integrated circuit is formed are placed on the test instrument, and whether each electronic component has a predetermined function is tested. At this time, each electronic component disposed on a tray or the like is carried to the test instrument by a transfer apparatus. Further, even when the electronic components are placed on the test instrument, a plurality of kinds of electronic components are carried to the printed circuit board sequentially in predetermined order by using the transfer apparatus.
As such a transfer apparatus, there has been well known an apparatus in which: a horizontally movable carrying head is provided with a sucker to be movable vertically; and the carrying head is moved to predetermined positions of a component supply stage and the test instrument; and the sucker is moved vertically at each predetermined position of the component supply stage and the test instrument. A suction/release passage, which is connected to a positive pressure source and a negative pressure source and opened to a contact face that contacts with the workpiece, is formed in the sucker so that, on the component supply stage, negative pressure is supplied to the suction/release passage and the sucker is brought into contact with the workpiece to suck the workpiece. After the workpiece is transferred to the predetermined position of the test instrument, the supply of the negative pressure to the suction/release passage is stopped to place the workpiece on the test instrument and positive pressure air for vacuum breakage is supplied to the suction/release passage so that the workpiece can be securely released from the sucker. Then, the carrying head, which has released the workpiece, returns to the component supply stage, and the transfer of the workpieces is repeated in the same procedure.
In such a suction/transfer apparatus, the transfer operation is performed after confirming that the workpiece has been sucked by the sucker in order to prevent missing or dropping of the workpiece during the transfer. As means for such suction confirmation, a conventional suction/transfer apparatus has a suction pressure sensor for detecting pressure in the suction/release passage, which detects the suction of the workpiece when a negative pressure value in the suction/release passage increases to or beyond its suction detection value during a suction operation. For example, the suction/transfer apparatus disclosed in Japanese Patent Laid-Open Publication No. 2001-54886 (pages 5-6 and FIG. 8) detects a suction-preparation pressure Pset when the negative pressure is supplied to the sucker, and detects the suction of the workpiece when the negative pressure value of the suction/release passage reaches suction detection pressure Pj obtained by adding a predetermined suction detection value ΔPset to this suction-preparation pressure Pset.
It is desirable in use that the suction/transfer apparatus can recognize the drop of the workpiece even during the transfer. However, in the above-described conventional technique, the release of the workpiece from the sucker is detected only when the negative pressure value of the suction/release passage is equal to or less than a release pressure value Preset set at negative pressure lower than the suction preparation pressure Pset. Therefore, even if the workpiece drops during the transfer and the sucker becomes in a state of sucking nothing, the negative pressure value of the suction/release passage is not reduced below the suction preparation pressure Pset, so that the drop of the workpiece cannot be recognized during the transfer.
Here, as means for securely detecting a suction/release condition of the workpiece, a recognition method by image sensor has been generally known. However, drop recognition by the image sensor is generally too expensive to be attached to a general-purpose suction/transfer apparatus, so that such an apparatus is difficult to use actually.
An object of the present invention is to be capable of securely detecting the drop of the workpiece from the sucker when the workpiece is transferred by the sucker.